The present invention relates to a gas detector for measuring the concentrations and presence of unwanted or combustible gases so that an alarm can be given when excessive concentrations of such gases are measured. More particularly, the invention relates to a ruggedized construction for a gas detector which houses a gas chamber and an infrared source and sensor for directing infrared radiation through the chamber to the sensor.
Infrared gas sensors have been widely used in the prior art for either detecting the presence of a gas or measuring the concentration of a gas in a particular environment. These devices use the principle that various gases exhibit substantial absorption at specific wavelengths in the infrared radiation spectrum. If an infrared source is positioned at some spatial distance from an infrared sensor, the amount of infrared energy at specific wavelengths which is absorbed between the source and the sensor provides a measure of particular gas concentrations in the intervening space. The infrared wavelength isolation is typically provided by utilizing narrow band infrared transmission filters which block all wavelengths outside of a predefined wavelength. The predefined wavelength is chosen to be a known wavelength which is absorbed by the particular gas which is being analyzed.
Gas detectors of the general type relating to this invention are particularly useful in detecting gas concentrations which are the byproduct of fires; and therefore, such devices become useful as fire detectors. They offer the advantages of relatively fast response, relatively high stability and sensitivity, and being capable of implementation in a simple structure. These advantages are particularly useful in designing gas detectors for use in a hostile environment, such as an industrial site. Such environments require a highly reliable and ruggedized construction wherein the gas detector may be easily maintained and capable of withstanding physical and environmental abuse. A number of different constructions for gas analyzers of the general type related to this invention are found in the prior art. For example, U.S. Pat. No. 5,341,214, issued Aug. 23, 1994, discloses a gas analyzer having a single infrared source and two detectors spaced apart in a chamber wherein the interior walls of the chamber reflect the radiation. U.S. Pat. No. 5,163,332, issued Nov. 17, 1992, discloses an infrared light source and detector separated at either end of an elongate chamber wherein the chamber has a plurality of openings to permit gas permeation into the chamber. U.S. Pat. No. 4,709,150, issued Nov. 24, 1987, discloses a similar type of gas analyzer wherein the chamber has a porous tube surrounding an enclosed column of air, the porous tube having openings sized to permit gas diffusion through the tube. U.S. Pat. No. 4,560,873, issued Dec. 24, 1985, discloses a combustion gas analyzer with an elongate probe for inserting into a flue or gas stack. An optical path is reflected through the elongate probe via a light source and a photocell to detect the presence of gas in the probe.
There is a need for a gas detector of the general type disclosed in the foregoing patents having an extremely rugged construction for permitting reliable operation in an industrial setting, and wherein the measurement chamber is protected from water and dust accumulation.